In order to maintain or improve manufacturing yield of products manufactured in a manufacturing line for semiconductor devices, a foreign material that is attached onto a substrate (wafer), a flaw that occurs on a surface of the substrate, defective crystal or the like is inspected during a process of manufacturing the semiconductor devices. For example, in order to manage dust in an etching device or a sputtering device, a dummy wafer that has a surface whose cleanness degree (the number of foreign materials, a distribution of the foreign materials on the surface, or the like) is known is placed in a process device, transported within the process device, and carried out of the process device after a dummy operation. Then, the surface of the wafer is inspected. The cleanness degree of the wafer surface is compared before and after the process. If it turns out that the number of foreign materials is increased with the process by the device, the operation of the device is stopped for cleaning and maintenance.
In a conventional semiconductor manufacturing process, the presence of a foreign material having several tens of nanometers in diameter could cause a reduction in the yield of manufacturing the semiconductors. In order to maintain high yield of manufacturing semiconductor substrates, it is significant to swiftly detect abnormality (occurrence of dust in a manufacturing device) in the manufacturing device and suppress defective products at work. In addition, for a device for inspecting a wafer surface, improving sensitivity (or detect a minute foreign material) of the device is highly demanded.
An example of the inspection device for such a purpose is disclosed in Patent Document 1. Patent Document 1 discloses a device configured to irradiate, with laser light, a surface of a rotating and translating wafer and detect scattered laser light scattered from a foreign material attached to the wafer surface. Patent Document 1 further discloses a method for processing a detected signal for the purpose of a high sensitivity. In the conventional example of Patent Document 1, a plurality of optical systems for detecting scattered light are arranged (in a plurality of azimuth directions and a plurality of elevation directions) around a point on the wafer that is to be irradiated with the laser light. The high sensitivity is achieved by applying directivity of a light component (background noise component) scattered due to roughness of the wafer surface to weighted adding process of a plurality of detected signals.
In addition, Patent Document 2 discloses a device configured to irradiate, with laser light, a surface of a rotating and translating wafer and detect light generated and scattered from a foreign material attached to the surface of the wafer. Patent Document 2 further discloses a method for causing a line sensor to detect light from regions formed by dividing a region irradiated with the laser light in the configuration of the device. In the conventional example of Patent Document 2, a plurality of optical systems for detecting scattered light are arranged (in a plurality of azimuth directions and a plurality of elevation directions) around a point on the wafer and is to be irradiated with the laser light. However, the line sensor that has multiple pixels is used as a light receiver. A light receiving surface of the line sensor is in a conjugate relationship with the position of the point on the wafer and is irradiated with the laser light. Thus, the position of the point on the wafer and is irradiated with the laser light is imaged and observed. A light component (background noise component) scattered due to roughness of the surface of the wafer is assigned to each of the pixels of the line sensor and detected. Thus, background noise that is detected for each of the pixels of the line sensor is reduced.
In addition, a high sensitivity is achieved by repeatedly detecting the same defect (foreign material) multiple times and summing detected signal components.
In addition, Patent Document 3 discloses an inspection device configured to irradiate a surface of a rotating wafer from an oblique direction with light linearly formed by a cylindrical lens, and with a CCD, detect light scattered in a direction perpendicular to a direction of extension of a linear region (irradiated with the light and laying on the surface of the wafer) or a direction oblique to the surface of the wafer and thereby detects a defect.
In addition, Patent Document 4 discloses the configuration of an optical system for observing, from an oblique direction, a surface of an object to be inspected.
In a conventional example described in Patent Document 4, a relay lens is located at an elevation of 30 degrees with respect to the surface of the object to be inspected, and an intermediate image of the surface of the object to be inspected is formed on a diffraction grating. The intermediate image is magnified by an objective lens that faces the diffraction grating, then, the intermediate image is observed by an image sensor. With the configuration, even when the surface of the sample is observed from an oblique direction at a different azimuth, fields of all observation optical systems can match each other. By optimizing a periodic structure (the number of grooves and blaze angles) of the diffraction grating, light that is incident on the diffraction grating is diffracted as first-order diffracted light in the normal direction of the diffraction grating and efficiently incident on the objective lens.